Thermal remediation can be used to treat hazardous wastes found at Superfund sites. These sites can incorporate chlorinated hydrocarbons and heavy toxic metals. The thermal treatment of these materials can release hazardous byproducts into the environment. This project seeks to determine the risk to human populations as a result of a release of chlorinated by-products or metals. The chlorinated compounds of most interest are the dioxins. The impact of the rate of mixing of waste and air on the formation of dioxins will be studied in a wind tunnel experiment. Samples of by-products will be collected for later analysis with the toxicology projects for the presence of dioxins. The focus of the metals will be collected for later analysis with the toxicology projects for the presence of dioxins. The focus of the metals research will be on chromium. Chromium is a non volatile metal that tends to form an ultrafine aerosol in high temperature systems. The hexavalent form of chromium is very toxic; the other valence states are not toxic. Hence, it is important to be able to predict the state of chromium emissions and to design systems to minimize the formation of the hexavalent form. This requires knowledge of the kinetics of chromium oxidation in combustion systems. A low pressure burner will be constructed to undertake experiments in a simple, laminar pre-mixed flame that is seeded with chromium. An on-line time of flight mass spectrometer will provide measurement of chromium intermediates. The results will be used to tune a kinetic model of chromium oxidation for application in the design of practical systems. Collaboration with the University of Colorado Boulder will permit laser induced fluorescence measurements of reactive intermediates to be undertaken. Modeling of the dynamics of the chromium aerosol will also be undertaken to predict the size of the aerosol particles. The toxicity of the particles may change as they age in the atmosphere. Artificial aging in a chamber will be used to simulate the reaction of particles in the atmosphere, on their way to human populations. The toxicity of the aged particles will be studied by analytical chemistry as well as by the various bioassays that are available to use throughout the Superfund program. The toxicity of the aged particles will be assessed in vitro, as well as in vivo with animal exposures to artificially condition combustion generated aerosols.